In an attempt to render pharmaceutical preparations or pesticides gradually releasable, extensive studies have been made of particulate or microcapsuled resin comprising a polyester, particularly a biodegradable polyester. For example, JP-A-6-72863 (The term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-8-157389, and JP-A-9-208494 disclose a technique concerning gradually-releasable pharmaceutical preparations comprising a lactic acid-based polymer as an aliphatic polyester.
These microcapsulization processes include a process which comprises adding a solution or dispersion obtained by dissolving a lactic acid-based polymer which doesn't have hydrophilic groups sufficiently in an organic solvent and dissolving or dispersing medicines in the solution dropwise to an aqueous solution containing a surface active agent, stirring the mixture to form an oil-in-water type emulsion or adding the solution or dispersion dropwise to an oil immiscible with the solution or dispersion, stirring the mixture to form an oil-in-oil type emulsion, and then evaporate the solvent away from the emulsion to solidify the microcapsule (submerged drying process) and a process which comprises stirring the foregoing solution or dispersion while a solvent miscible with the solution or dispersion but incapable of dissolving the polymer (so-called poor solvent) is being added thereto so that the polymer undergoes phase separation to prepare a microcapsule (coacervation process).
The microcapsule obtained by these preparation processes comprises a constituent polymer which doesn't have hydrophilic groups sufficiently as defined herein and thus doesn't exhibit so-called self-water dispersibility. Thus, the addition of an auxiliary such as surface active agent during the preparation of microcapsule is indispensable. High speed agitation is required as well. Further, it is difficult to prepare extremely small particles having a size of the order of nanometer.
JP-A-6-313024 discloses a technique concerning an aqueous polyurethane resin prepared by neutralizing with a base a lactone-based polyurethane resin having a carboxylic acid comprising a lactone-based polyester polyol obtained by ring opening polymerization of lactone in the presence of a dihydroxycaboxylic acid as an initiator, a diisocyanate and a chain extender.
The above proposed method can provide a self-water dispersible particle as well. However, this method doesn't allow two or more carboxyl groups to be introduced into molecular chain unless diisocyanates, which are undesirable for living body or environment, are used. Further, in order to reduce the particle size of the particulate material to an extent such that it is rendered self-water dispersible, it is necessary to raise the acid value in the polymer. To this end, the particulate material needs to contain a large amount of urethane bond. Accordingly, the desired physical properties of polyester can be hardly maintained, causing deterioration of biodegradability.
Many methods for the preparation of capsulized pesticides obtained by microcapsulizing pesticide activator components have been known. For example, JP-A-6-362, JP-A-6-238159, JP-A-7-165505, JP-A-8-53306, JP-A-9-249505, and JP-A-9-57091 disclose a method for the preparation of capsulized pesticides by interfacial polymerization method using polyurea or polyurethane as a wall material.
Further, JP-A-5-155714 discloses a method for the preparation of capsulized pesticides involving the copolymerization of an unsaturated polyester resin with a vinyl monomer in the presence of a hardening initiator. JP-A-5-70663 discloses a method for the preparation of capsulized pesticides comprising acryl copolymer. All these methods comprise emulsion-dispersing a resin and a chemical in water, and then allowing the dispersion to undergo polymerization at particle interface or inside the particles to prepare a capsulized pesticide. An emulsifying agent is essential to disperse these components in water.
It has thus been desired to develop a particulate self-water dispersible biodegradable material having an average particle diameter as small as nanometer free of urethane bond and excellent in biodegradability, and a process for the preparation of a particulate self-water dispersible biodegradable material without using any isocyanate which is undesirable for living body or environment or emulsifying agent and any high rotary speed agitator.